In the field of Third Generation Partnership Project Long Term Evolution (3GPPLTE), a control channel (L1/L2 control channel) for signaling and quality information notification is set between a radio terminal (terminal, called as user equipment: UE) and a radio base station (base station, called as eNode B) that are in a synchronized state. In order to request the base station to allocate a radio resource, the terminal uses an uplink control channel (L1/L2 control channel, physical uplink control channel: PUCCH) to issue a scheduling request (SR) as a radio resource allocation request message.
For example, in 3GPP LTE, the cycle and timing of SR transmission from the terminal are determined in advance in the base station and the terminal. In the case where the terminal, upon reaching the SR transmission cycle, is holding user data to be transmitted to the base station, the terminal transmits an SR to the base station. On the other hand, in the case where the terminal reaches the SR transmission cycle and is holding no user data to be transmitted at that point, the terminal does not transmit an SR.
On the base station side, control information including an SR may be received over the uplink control channel (UL L1/L2 control channel) according to the predetermined cycle and timing of SR transmission in the terminal. Receiving control information from the terminal, the base station analyzes the control information including an SR. The base station determines the allocation of an uplink radio resource to the terminal based on the result of the analysis. The base station then issues and transmits a message (scheduling grant: SG) for notifying the terminal of a radio resource allocation result (radio resource allocation information).
Receiving the SG issued from the base station, the terminal may transmit data to the base station with the use of a radio resource allocated according to radio resource allocation information that is contained in the SG.
In the uplink from the terminal to the base station, quality information (called as channel quality indicator (CQI)) is transmitted and received over the uplink control channel as control information that is not the SR described above. A CQI is used by the base station to keep track of the quality of the terminal and to execute control for ensuring the quality of communication with the terminal. An SR is used by the terminal to request the base station to allocate a radio resource for transmitting data when there is data to be transmitted to the base station.
As illustrated in FIG. 24, for example, the terminal is allocated a radio resource for an uplink control channel in a fixed given cycle. A radio resource for CQI transmission is allocated for each cycle. As control information that is not a CQI, parameters such as radio bearer group buffer status (RGBS: transmission buffer retention amount) and user equipment power headroom (UPH) are transmitted in the same transmission cycle as CQIs. For SRs, on the other hand, a transmission cycle longer than the CQI transmission cycle is fixedly defined, and an SR is transmitted by spending a domain that is intended to store a CQI.
[Patent document 1] Japanese Laid-open Patent Publication No. 2007-53747
Basically, an SR needs to be transmitted from the terminal to the base station only when the terminal has transmission data to be transmitted. However, the transmission of an SR from the terminal to the base station requires the allocation of an uplink radio resource for SR transmission. The base station side has no means of knowing when transmission data is held in the terminal and when the terminal is going to transmit an SR. This is why at present an uplink radio resource for SR transmission is allocated fixedly and cyclically to every terminal.
A drawback is that, because the terminal side does not transmit an SR to the base station when there is no transmission data, a radio resource allocated for SR transmission is wasted when the terminal does not transmit an SR.
Another drawback is that, because a radio resource for SR transmission utilizes part of a radio resource for CQI transmission as described above, the size of CQI information in an SR transmission cycle is limited by the SR. The terminal side therefore takes such measures, at least in an SR transmission cycle, as simplifying CQI information and postponing the transmission of part of CQI information until a subsequent cycle. Consequently, compared to when a radio resource for SR transmission is not allocated, the resolving power in terminal quality control on the base station side is lowered and the arrival of part of CQI information is delayed, which may deteriorate the quality of communication between the base station and the terminal.
Further, unnecessary SR transmission presents interference to other terminals, and may lead to deterioration in communication quality and a reduction in the maximum connected terminal count of the base station.
It is therefore desirable to increase the amount of radio resource allocated for CQI transmission while making the amount of radio resource allocated for SR transmission from the terminal to the base station as small as possible.
For example, consider improving the communication quality by uniformly stretching SR transmission cycles. In this case, however, a delay counted from the time when data to be transmitted is held in the terminal to the time when the terminal transmits an SR to the base station increases. The increase in data transmission delay is caused by the delayed allocation of an uplink radio resource to the terminal on the base station side. Furthermore, data stays for a longer period of time in a transmission buffer of the terminal, increasing the probability of data discard due to buffer full. Installing more transmission buffers leads to a rise in cost. Even with additional transmission buffers, the aforementioned problems of increase in delay, longer data stay in buffers, and data discard due to buffer full are not solved when the data communication rate is high.